A known load detecting apparatus for detecting external load (externally applied load) by a strain (displacement) is disclosed in JP2003-83707A (hereinafter referred to as reference 1). According to the reference 1, a detecting member is press-fitted into a detection hole formed at a sensor substrate (strain member) and the external force is acted on an end portion of the detecting member, at which the detecting member comes in contact with the sensor substrate. Further, first and second fixing members (supporting members) are press-fitted into first and second fixing holes formed at the sensor substrate, respectively. Then, counter force is generated at end portions of the first and second fixing members, at which the first and second fixing members come in contact with the sensor substrate. The load detecting apparatus detects strain generated due to the external force and the counter force by means of strain detecting elements.
Further, according to a load detecting apparatus disclosed in WO2005/080931A1 (hereinafter referred to as reference 2), a fixing member (supporting member) is structured with an upper washer and a lower washer. The upper washer is press-fitted into the lower washer, thus supporting (interposing) a sensor substrate. Accordingly, the fixing member is fixed to the sensor substrate. Further, strain detecting elements are provided on the sensor substrate. The load detecting apparatus structured as above is secured to an object to be measured via the supporting member.
According to the structure of the load detecting apparatus disclosed in the references 1 and 2, because the fixing member(s) is press-fitted into the sensor substrate and is secured thereat, strain may be generated at positions adjacent to the fixing member(s) on the sensor substrate (a portion of the substrate adjacent to the fixing member) due to the force for press-fitting the fixing member(s) into the sensor substrate. Therefore, in a condition where the strain detecting elements are to be positioned in the vicinity of the fixing members, a value outputted from the strain detecting elements may be deviated from a zero point (a point of origin), and detecting accuracy (sensitivity) may be negatively affected because of influence of the generated strain, thus leading to a reduction of precision for detecting the external load.
A need thus exists for a load detecting apparatus which is not susceptible to the drawback mentioned above.